Maharashtra BoardEnglish MediumSTD 11 ScienceBiologyPhotosynthesis5 Marks
Question
Differentiate between $PS-I$ and $PS-II.$
✓
Answer
$1.$ The movement of ions across a selectively permeable membrane, down their electrochemical gradient is called chemiosmosis.
$2.$ The movement of hydrogen ions across a membrane during cellular respiration in mitochondria and during photosynthesis in chloroplasts, leads to the generation of $\text{ATP}.$
$3.$ These membranes are thylakoids and the protons accumulate in the lumen during photosynthesis.
$4.$ An electrochemical concentration gradient forms when hydrogen ions $($protons$)$ diffuse from an area of higher proton concentration to an area of lower proton concentration.
$5.$ This electrochemical concentration gradient of protons across a membrane can be utilized to make $\text{ATP}.$
$6. \ \text{ATP}$ synthase is the enzyme that makes $\text{ATP}$ by chemiosmosis. .
$7.$ It allows protons to pass through the membrane using the kinetic energy to phosphorylate $\text{ADP}$ making $\text{ATP}$.
$8.$ Splitting of water molecule on the inner side of the membrane results in the accumulation of hydrogen ions within the lumen of thylakoids.
$9.$ The enzyme, $\text{NADP}$ reductase, is located in the stroma side of the membrane.
$10.$ For reduction of $\text{NADP}$ to $NADPH_2$ protons are required along with electrons that come from ferredoxin.
$11.$ Thus, within the chloroplast, the protons in the stroma decrease in number, while in the lumen, the number of protons increases.
$12.$ This creates a proton gradient across the thylakoid membrane.
$13.$ Energy,generated by the subsequent spontaneous movement of protons is used for the synthesis of $\text{ATP}.$
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